Composite material leaf springs are known and typically comprise a filler material, for example glass roving or other filamentary solids, in an organic resin matrix such as thermoplastic or, more typically, thermosetting plastic. Such springs are known, for example, in U.S. Pat. Nos. 2,600,843, 2,829,881, 3,142,598, 4,489,922 and 4,575,057. Known methods of making composite material leaf springs include, for example, filament winding, compression molding and pultrusion.
In the past, composite material leaf spring have been used in motor vehicle suspension systems with associated hardware to hold the spring accurately in position. Such spring clamping hardware has been fashioned after hardware previously known for use in conjunction with metal leaf springs. In a typical arrangement, the spring is positioned between a clamping plate on one side and the axle or other wheel carrying member on the other side. Often, a second clamping plate or the like is positioned between the spring and the axle to act as a spring seat. Bolts or the like, for example, U-bolts, are used to clamp the clamping plate and spring to the axle An abrasion resistant pad can be used between the spring and the axle (or spring seat) Exemplary clamping hardware for a composite material leaf spring is seen, for example, in U.S. Pat. Nos. 3,968,958, 3,586,307 and 3,541,605.
Known leaf spring clamping hardware has been found inadequate in certain respects for use in conjunction with composite material leaf springs Specifically, such spring clamping hardware has been found inadequate to hold the spring in a fixed Position relative the axle under conditions experienced in ordinary use. More specifically, known spring clamping hardware often has failed to prevent longitudinal movement of the spring, that is, movement of the spring in a direction along its longitudinal axis (which typically is transverse to the longitudinal axis of the axle). Movement of the composite material leaf spring relative the axle or other wheel carrying member in a direction along the longitudinal axis of the leaf spring would change the pivot point of the leaf spring against the axle. Consequently, the spring rate would be altered and the spring would fail to perform according to design. Moreover, upon flexure of the spring, the compressive and tensile stresses would be improperly distributed, which could lead to increased material fatigue and decreased spring life. Moreover, if excessive, such movement could lead to damage to a vehicle powertrain.
A leaf spring clamp suitable for use with a composite material leaf spring is disclosed in commonly assigned U.S. Pat. No. 4,519,590 to W. E. Wells. Therein, a leaf spring axle clamp assembly is disclosed to comprise a rigid clamp base which forms a channel to jacket the leaf spring, and a resilient insert which is inserted between the leaf spring and the rigid clamp base. The resilient insert fills substantially entirely the space between the leaf spring and the rigid clamp base and employs friction and a wedge effect to prevent longitudinal movement of the leaf spring. In commonly assigned U.S. patent application Ser. No. 689,364, patented 12/23/86 U.S. Pat. No. 4,630,804, a similar leaf spring axle clamp assemble is disclosed in which the resilient insert(s) provide voids above the below the leaf spring to accommodate the bending displacement of the leaf spring within the axle clamp assembly. It was found that displacement of the leaf spring within the clamp, especially large bending displacements of the spring, is disadvantageously impeded by the resilient insert without such voids. The resilient insert cannot be eliminated since the leaf spring must be effectively isolated from rigid clamp parts to prevent abrasion and crushing damage to the synthetic material of the spring.
In regard to the aforesaid composite leaf spring clamp assemblies which employ resilient wedge inserts, a measure of compressive pre-load is exerted on the resilient inserts in the assembled axle clamp. The inserts are placed under a compressive pre-load when the clamp plate and clamp base are attached to each other around the resilient wedge inserts and the leaf spring. Such compressive pre-load best achieves the aforesaid friction and wedge effect to secure the leaf spring properly in position within the axle clamp. To achieve such compressive pre-load, U-bolts can be employed to hold the rigid clamp plate and clamp base together (or a pre-selected distance apart), with the resilient inserts (and leaf spring) sandwiched between them. The torque applied in tightening the U-bolt nuts determines the level of pre-load This feature, however, has been found to present certain difficulties in achieving consistent pre-loading of the clamps during initial assembly. In addition, there is the risk that U-bolt nuts might inadvertently loosen Over time it has been found that the degree of pre-load within the axle clamp assembly can significantly affect the performance characteristics of the leaf spring. Thus, there is a need for a leaf spring clamp of the subject type in which the correct pre-load can be easily achieved and maintained during use over time. On such leaf spring clamp is disclosed in U.S. patent application Ser. No. 803,753, filed Dec. 2, 1985, U.S. Pat. No. 4,684,110, patented on Aug. 4, 1987, in the name of R. F. Sale and W. E. Wells. Therein, the clamp plate and clamp base are provided with corresponding tabs and slots. For assembly of the axle clamp, the tabs are best around into the slots. Such tab-and-slot feature, however, is not readily applicable to axle clamp assemblies employing a clamp plate and clamp base formed of cast metal, such as cast iron. Nevertheless, the use of cast metal components would be advantageous in certain applications in view of their rigidity and strength.
It is an object of the present invention to provide a leaf spring clamp which secures a leaf spring, especially a filament reinforced composite material leaf spring, in position in a suspension system. It is a particular object of the invention to provide an axle clamp assembly which does not require either damage to or dislocation of either the reinforcing filaments or the resin matrix of the leaf spring and, specifically, which does not require a hole through the leaf spring or concavities in the surface of the leaf spring or other complexities in the shape of the leaf spring.
Additional objects and advantages of the invention will be apparent from the following disclosure.